Cathode ray tube



Dec. 29, 1942. w. HEIMANN ET AL CATHODE RAY TUBE Filed March 29, 1940 Fly. 1

Invenfars iatented Dec. 29, 1942 CATHODE RAY TUBE Walter Heimann and Kurt Wemheuer, Berlin,

Germany; vested in the Alien Property Custodian Application March 29, 1940, Serial No. 326,606 In Germany December 15, 1938 Claims.

This invention is concerned with an arrangement for converting an optical image into an electron image. More particularly, the invention relates to those devices of this kind in which the electron-optic reproduction of the optical image is effected with the aid of electric lenses.

As is well known, by shaping the cathode and anode appropriately the accelerating field between the two may be so adjusted that it shall be able by itself to depict or reproduce a somewhat large area of the cathode. This result is comparatively easy to attain with vaulted or curved surfaces of the cathode. In the case, however, of a plane surface employed as cathode it is difficult to produce an undistorted and sharp reproduction of a circular image area whose diameter is larger than three centimeters.

Investigations which have resulted in the invention have shown that, especially for reproducing a somewhat large area, the potential lines or surfaces concerned with the image reproduction should not in any way run parallel to the optical axis of the system. In prior arrangements they are to a considerable extent parallel thereto.

In order to avoid this the invention provides for using the cathode as a guide for the equipotential surfaces, as will be understood from the following description, reference being had to the accompanying drawing, in which Fig. 1 is a partially diagrammatic sectional view representing one embodiment of the invention, while Fig. 2 is a fragmentary sectional view showing a slight modification of the arrangement illustrated in Fig. 1.

In Fig. 1 K denotes a photo-sensitive cathode which is a hollow body composed of a cylindrical wall e and two plane discs I, 9. Disc ,f, on which an optical image is produced in conventional manner, is to be depicted on the fluorescent screen S of a bulb B, the aim being to depict the largest possible area thereof. An electrode A, which is the so-called accelerating anode made in the shape of a hollow cylinder, is arranged to project into the cathode K through an aperture provided in the disc g.

P indicates a potential line within the cathode space, that is, the interior of the cathode K. This line comprises two parts, shown dotted, which are most remote from the optical or longitudinal axis Q and are somewhat parallel to this. These two parts are not intended to cooperate in the process of producing the image on screen S.

It will thus be seen that the diameter d1 of the cathode must be larg enough in relation to the length Z thereof as well as in relation to the diameter d2 of the anode A. 111 should be at least double the length Z. The aperture through which the anode A projects into the cathode K is somewhat larger than diameter (la. The small interspace so provided between disc g and anode A is dimensioned to correspond to the voltages employed in the respective case.

A further improvement is obtained by giving the cathode the shape shown in Fig. 2. The cathode K there represented has no corners while its face ends are slightly curved.

The image on screen S will be still further freed from distortion if the anode is given the form shown in Fig. 2. The anode A there represented has one end provided with a funnel-shaped contraction b located within the cathode space in order to cause the edge lines of the potential field to cling to the anode.

In Fig. 1 also the metal coating M is shown which is either connected with the anode A or is given a potential with respect to it so that A and M constitute a lens which may serve to correct in geometrical relation the image on screen S.

What is claimed is:

1. In a cathode ray device for converting an optical image into an electron image, photo-sensitive cathode disc adapted to receive an optical image, a screen for receiving an electron image of the optical image on said disc, a hollow cylindrical anode for accelerating the image forming electrons from said disc, a hollow electrode element forming a guide wall extending axially of said device from edge of said disc toward said screen and enclosing the space near said disc through which said image forming electrons travel from said disc, a second disc forming a partial closure for the end of said hollow electrode element, said second disc being remote from said photo-sensitive disc and spaced therefrom along the axis of said device in the direction toward said screen and having an axial aperture therein of larger diameter than said accelerating anode.

2. A cathode ray device according to claim 1 in which said discs and said guide wall element are joined together to form a hollow cathode electrode having an aperture of a diameter smaller than that of said photo-sensitive disc but of larger diameter than that of said accelerating anode.

3. A cathode ray device according to claim 1 in which said guide wall is a cylinder having a diameter at least double th axial length thereof.

4. A cathode ray device according to claim 1 in which said accelerating electrode projects into the aperture of said second disc, and is of slightly smaller diameter than said aperture.

5. A cathode ray device according to claim 1 in which an electrode surrounds said accelerating anode and forms an electron lens element in cooperation therewith to correct the image on said screen.

WALTER HEIMANN. KURT WEMHEUER. 

